<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
   let a ={m:1}
   let b = a
    // a.m = 2
    // console.log(b.m);//2
    // a={m:2}
    // console.log(b.m);//1
    function fn(a){
   //   a={m:2}
      a.m=2
     console.log(a.m)
    }
    fn(a)


  console.log(a.m,b.m)//1,1
    //  let a={m:1}
    //  let b=a
     
  </script>
</body>
</html>